This invention relates to high-capacity elastomeric bearings, and more particularly to elastomeric bearings for use when the axial and/or radial loads are high and the torsional oscillations are small.
Conventional tapered roller or spherical roller bearings have not given adequate life in applications such as wind turbine blade teeter systems and offshore mooring systems, where axial and/or radial loads are high and torsional oscillations are small. Conventional high-capacity elastomeric laminate bearings have been successful, but they have required up to a fifty percent larger space envelope than the roller bearings.
FIG. 1 and FIG. 2 illustrate cross-sectional views of prior art conventional high-capacity elastomeric laminate bearings. Referring now to FIG. 1, a combination stacktube bearing is illustrated. Inner bearings 10 are referred to in the industry as "stack form" bearings. In wind turbine applications the stack form bearings 10 bear the axial loads or forces 11 (the weight of a blade rigidly attached to a teeter pin 14). Outer bearings 16 are referred to in the industry as "tube form" bearings. The tube form bearings 16 bear the radial loads or forces 17 (the weight of a blade plus the torque exerted by the blade/teeter pin combination against a yoke 18). Both bearings 10 and 16 are made of an elastomer such as silicone, natural rubber, polybutadiene, nitrile, or neoprene.
It is well known in the art that the spring rate of the stack form bearings 10 (the axial spring rate) should be matched as closely as possible with the spring rate of the tube form bearings 16 (the radial spring rate). This is required to keep the deflection across each bearing equal in order to minimize the bobbing of the blades as they rotate. The bobbing of the blades increases fatigue on the elastomer. However, in some applications, it has not been possible to achieve the desired matching of the axial and radial spring rates and still keep the overall dimensions of the combination stack-tube bearing within the desired limits.
Therefore, some have attempted to solve this problem with the conical bearing illustrated in FIG. 2. However, the conical bearing illustrated in FIG. 2, although its overall dimensions could be made smaller, wore out quickly when sized to the same dimensions as a metal bearing, because due to the geometry, the elastomer strain levels were not uniform.
Existing prior art formulas for predicting axial and radial spring rates were based on mathematical assumptions applicable only to the type of bearings illustrated in FIG. 1 and FIG. 2. Therefore, no formula applied to the unique configuration of the present invention. Thus, a finite element computer program was used to evaluate (as is common in the industry) the unique configuration of the present invention, and to calculate the axial and radial spring rate constants.
The present invention addresses the above-noted and other drawbacks to the prior art by providing an apparatus for a high-capacity elastomeric combination journal-thrust bearing which achieves the durability of the elastomeric laminate bearings. This invention eliminates the undesirable feature common to the laminate bearings of the type illustrated in FIG. 1, wherein the laminate bearings require up to a fifty percent larger space envelope than the conventional tapered roller or spherical roller bearings. The invention is believed to be the first elastomeric bearing which can achieve a closer matching of axial and radial spring rates than achieved by the larger prior art elastomeric laminate bearing of FIG. 1, and yet the bearing of the present invention fits into the same space envelope as the double cylindrical roller and double tapered roller bearings it replaces.
The high-capacity elastomeric combination journal-thrust bearing built according to the present invention comprises an encapsulated lobe. The encapsulated lobe comprises an outer tubular member, an inner tubular member, rings joined to the inside of each end of the outer tubular member, a third ring spaced between the first two rings, and an elastomer. The third ring is joined along its inner periphery to the outside of the inner tubular member. The elastomer joins the first and second rings to the inner tubular member, the third ring to the outer ring, the third ring to the first and second rings, and the inner tubular member to the outer tubular member. As the radial distance from the longitudinal axis of the tubular members increases, the thickness of the elastomer increases.
In yet another feature of the invention, the bearing comprises a plurality of encapsulated lobes.